1. Field of the Invention
The present invention relates generally to internal combustion engines. More particularly, the present invention relates to a piston cooling system in an internal combustion engine, in which oil is jetted to a piston to provide a cooling effect, where the piston is adapted to reciprocate in a cylinder bore.
2. Description of the Background Art
In a conventional piston cooling system of an internal combustion engine, an oil jet is normally provided on a journal wall that journals a crankshaft. Oil discharged from an oil pump is directed to the oil jet, and the cooling oil is directly jetted from the oil jet to a piston which is reciprocating in a cylinder bore. By doing so, the piston is cooled. Such a conventional piston cooling system is disclosed, for example, in JP-A No. 2003-74347.
The piston cooling system disclosed in JP-A No. 2003-74347 is applied to a multi-cylinder internal combustion engine, and oil discharged from an oil pump provided to a crankcase is directed to a main gallery formed in the crankcase via an oil filter and an oil cooler. The oil is distributed from the main gallery to a branch oil supply passage formed in each journal wall, is supplied to each journal bearing, and a portion of the oil is jetted to a piston from an oil jet provided in a journal wall.
Since the oil pump is driven using the rotation of a crankshaft as a power source, it is difficult to supply oil in a stable manner to the oil jet because the rotating torque of the oil pump periodically varies and the discharge pressure of oil pulses. Moreover, it is difficult to minimize the quantity of oil supplied to cool the piston and to effectively and efficiently jet oil from the oil jet.
The invention is made in view of the above described problems, and the object of the invention is to provide a piston cooling system of an internal combustion engine where oil is effectively jetted from an oil jet, and a piston can be efficiently cooled.